Plating Bath Filtration: Questions and Answers

Question:

One of our customers recently performed an audit of our plating operations and asked for information regarding the filtration specifications used for each of our plating baths. While we were able to answer the question in a manner that satisfied our customer, we decided to review our filtration processes on all of our plating baths. Can you supply us with some information so we know where to start? We have the following plating baths: Sulfate copper, Watts nickel, trivalent chromium and cyanide gold.

Answer:

Filtration of plating baths is a critical part of plating bath maintenance. Unfortunately many plating operations only review filtration processes when they find dead fish and debris floating in the plating bath.

The table below gives some basic data for filtration of the plating baths you are using. The data is courtesy of Serfilco, Ltd.

There is more to filtration than just the proper filtration media, micron size and turnover rates. Carbon treatment is also part of the equation and here we get into the issue of classical batch treatment versus continuous treatment. Space limitations do not allow for a complete discussion of this topic but it is suffice to say that batch treatment is messy, wastes part of your plating solution and if not performed properly, can lead to rough deposits. This approach has been used when the plating solution has become “overloaded” with what I call “trash” organic materials. This trash material is a by-product from the decomposition of the various additives that are added to modern plating baths. Continuation carbon filtration is a better method for doing this but comes with a price: it will remove the “trash” but also removes some of the good additives. The problem can be partially alleviated by setting up a filtration system that filters out particles at a rapid turnover rate and filters out organics at a much lower turnover rate.

More information on this subject can be obtained by contacting vendors listed in the Products Finishing Directory & Technology Guide. The Directory also contains a good article on the basic principles of filtration, titled "Solution Filtration".

Plating Bath	Turnovers (per hour)	Surface Area (ft2/100 gallons)	Micron Density	Recommended Media Fiber/Core
Sulfate copper	2 - 6	11 - 14	5 - 15	Polypropylene/stainless steel
Watts nickel	2 - 5	7 - 11	5 - 15	Polypropylene/polypropylene
Trivalent chromium	2 - 4	11 - 14	5 - 15	Polypropylene/polypropylene
Cyanide gold	2 - 4	7 - 11	5 - 15	Polypropylene/polypropylene

 

Question:

I have been given the task of evaluating and upgrading the filtration processes on our plating tanks. While I understand the basic principles involved I do not have a good understanding of the process as applied to plating baths. Can you provide me with some information on this topic? 

Answer:

Most everybody in our industry understands that filtration is a necessity in today’s plating environment, but many platers really do not have a good grasp of what is really involved. I recommend that you start your “filtration training” by reading the chapter on Solution Filtration in the 2002 PRODUCTS FINISHING DIRECTORY AND TECHNOLOGY GUIDE. Another useful article can be found in the Metal Finishing 2002 Guidebook & Directory. You can also get good information from vendors in the Suppliers section of the webisite. Look under Filtration Equipment, solution.